What was going on with the man behind WA head-on fatality

THE man filmed driving a four-wheel-drive erratically in Western Australia that crashed in a fatal head-on collision had been attempting to "start over again" after a "very bad year".

The driver, identified as Shaun Southern, was filmed driving a green Toyota Landcruiser along the Bussell Highway in Capel, a town in southwest WA, on Saturday.

Witnesses described the man behind the wheel as "crazed" and "going nuts" in his car.

The rampage ended when the apparently out-of-control Landcruiser swerved into the path of oncoming traffic, driving on the wrong side of the road before ploughing into a white Rav4 killing driver 61-year-old Jenni Pratt, and injuring her passenger, Karen Williams, 54.

Mr Southern was also hospitalised following the deadly crash in a critical condition.

Homicide detectives are awaiting improvements in his condition so he can be formally interviewed.

Capel car crash on Bussell Highway in WA's south west.Kate Sheedy

According to The West Australian the 45-year-old had been living alone in a caravan park on the outskirts of Bunbury, close to Perth.

The man is understood to be a divorced father of two children, and was employed as a fly-in, fly-out worker in the Pilbara.

Social media posts from Mr Southern indicate he recently moved in to a Bunbury carpark after being evicted from another caravan park in the coastal town of Leeman. He was believed to be having financial problems that led to him being unable to pay rent, telling friends he had lost money in what was a "long story".

In a Facebook post published in August Mr Southern said he had had a "very very bad year so far", and was moving and "starting over again".

He had been seeking casual work and selling off his belongings.

Since the incident, the man's social media profile has become a log of hateful messages with friends and strangers posting messages wishing the man would "die in prison" and "burn in hell".

Shaun Southern indicated he had been struggling financially.Facebook

Other commenters intervened suggesting Mr Southern be left alone "for his children's sake".

On the day of the crash Mr Southern was seen fishing on Wonnerup beach, north of Busselton.

One woman who claimed to have seen him earlier in the day said his behaviour was concerning and that she had called the police, while another account suggested he did not appear agitated.

Mr Southern had not been wearing a seatbelt when he was seen driving completely erratically on Saturday ahead of the 4.45pm crash.

A witness who was first at the scene of the fatal crash said he had been following the car for around 10 minutes because he was worried an innocent person would be hurt.

Dylan Mateljan began filming the Landcruiser after calling police capturing terrifying vision of the car taking out street signs and forcing other vehicles off the road.

Witnesses said it appeared the driver looked like he was "trying to hit someone".

Ms Pratt was unable to escape the path of the vehicle before it smashed into her Rav4 and exploded in a fireball.

Jenni Pratt died in the crash near Capel in WA.Channel 7

The TAFE worker has been remembered as a woman who "always saw the best in everyone".

"Mum's brightness, beautiful smile and the way she listened and cared, meant that so many people lived and relied on her as a companion, someone to confide in and a true friend," a statement provided by her family said.

Mr Southern was flown to Royal Perth Hospital where he remains in a critical condition and is expected to survive.

It is understood the investigation is being handled by homicide detectives, who await Mr Southern's recovery so he may be interviewed.

It has been suggested a murder charge will be considered.

Police continue to seek information from anyone who saw Mr Southern in the days leading up to the crash, and witnesses of the incident.